JDK-8297605 DelayQueue javadoc is confusing

[viktorklang-ora]

Clarifies the distinction between expiration of the head of DelayQueue and how it relates to poll, take, and peek. See discussion on https://bugs.openjdk.org/browse/JDK-8297605

@DougLea If possible, please weigh in on whether this is in line with your thoughts on the matter.

---

Progress

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Integration blocker

 ⚠️ Title mismatch between PR and JBS for issue JDK-8297605

Issues

• JDK-8297605: improve DelayQueue removal method javadoc ⚠️ Title mismatch between PR and JBS. ⚠️ Issue is already resolved. Consider making this a "backport pull request" by setting the PR title to Backport <hash> with the hash of the original commit. See Backports.
• JDK-8304686: improve DelayQueue removal method javadoc (CSR)

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[viktorklang-ora]

Updated version of #12727

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[mlbridge]

Webrevs

• 01: Full - Incremental (df54e8a7)
• 00: Full (6ef82915)

[DougLea]

Thanks. Adding the word "expired" (plus other adjustments) seems to be the simplest way to avoid confusion.

[Martin-Buchholz]

I like introducing the concept of "expired head".
Aren't we defining "expired head" here, not "head"?

[viktorklang-ora]

@Martin-Buchholz I read the line before the removed line (The head of the queue is that {@code Delayed} element whose delay expired furthest in the past.) as defining that the head will be the thing with the "soonest" expiry, which is important if one is used to LIFO or FIFO. Any idea on how we could improve that sentence? 🤔

[Martin-Buchholz]

I like extending this approach as follows:

• define "head"
• define "expired head"
• make it clear that some methods operate on all elements (regardless of their expiration status), some only on expired elements.
• ensure that all public methods have an overriding javadoc that makes the distinction clear. e.g. currently remove() needs such an overriding javadoc.
  (writing good spec is hard work!)

[Martin-Buchholz]

Here's my attempt:

 * An unbounded {@linkplain BlockingQueue blocking queue} of {@link Delayed}
 * elements, in which an element generally becomes eligible for removal when its
 * delay has expired.
 *
 * <p>An element is considered <em>expired</em> when its {@code
 * getDelay(TimeUnit.NANOSECONDS)} method would return a value less than or
 * equal to zero.
 *
 * <p>An element is considered the <em>head</em> of the queue if it is the
 * element with the earliest expiration time, whether in the past or the future,
 * if there is such an element.
 *
 * <p>An element is considered the <em>expired head</em> of the queue if it is
 * the <em>expired</em> element with the earliest expiration time in the
 * past, if there is such an element.
 * The <em>expired head</em>, when present, is also the <em>head</em>.
 *
 * <p>While this class implements the {@code BlockingQueue} interface, it
 * intentionally violates the general contract of {@code BlockingQueue}, in that
 * the following methods disregard the presence of unexpired elements and only
 * ever remove the <em>expired head</em>:
 *
 * <ul>
 * <li> {@link #poll()}
 * <li> {@link #poll(long,TimeUnit)}
 * <li> {@link #take()}
 * <li> {@link #remove()}
 * </ul>
 *
 * <p>All other methods operate on both expired and unexpired elements.  For
 * example, the {@code size} method returns the count of all elements.  Method
 * {@link peek()} may return the non-null <em>head</em> even when {@code
 * take()} would block waiting for that element to expire.
 *
 * <p>This queue does not permit null elements.

[openjdk]

@viktorklang-ora Please do not rebase or force-push to an active PR as it invalidates existing review comments. Note for future reference, the bots always squash all changes into a single commit automatically as part of the integration. See OpenJDK Developers’ Guide for more information.

[viktorklang-ora]

Here's my attempt:

 * An unbounded {@linkplain BlockingQueue blocking queue} of {@link Delayed}
 * elements, in which an element generally becomes eligible for removal when its
 * delay has expired.
 *
 * <p>An element is considered <em>expired</em> when its {@code
 * getDelay(TimeUnit.NANOSECONDS)} method would return a value less than or
 * equal to zero.
 *
 * <p>An element is considered the <em>head</em> of the queue if it is the
 * element with the earliest expiration time, whether in the past or the future,
 * if there is such an element.
 *
 * <p>An element is considered the <em>expired head</em> of the queue if it is
 * the <em>expired</em> element with the earliest expiration time in the
 * past, if there is such an element.
 * The <em>expired head</em>, when present, is also the <em>head</em>.
 *
 * <p>While this class implements the {@code BlockingQueue} interface, it
 * intentionally violates the general contract of {@code BlockingQueue}, in that
 * the following methods disregard the presence of unexpired elements and only
 * ever remove the <em>expired head</em>:
 *
 * <ul>
 * <li> {@link #poll()}
 * <li> {@link #poll(long,TimeUnit)}
 * <li> {@link #take()}
 * <li> {@link #remove()}
 * </ul>
 *
 * <p>All other methods operate on both expired and unexpired elements.  For
 * example, the {@code size} method returns the count of all elements.  Method
 * {@link peek()} may return the non-null <em>head</em> even when {@code
 * take()} would block waiting for that element to expire.
 *
 * <p>This queue does not permit null elements.

I think that approach sounds good. @DougLea, any opinion on this class javadoc summary?

[DougLea]

Yes, lgtm!

[viktorklang-ora]

@Martin-Buchholz Martin, how would you like to proceed with your proposed wording, would you prefer a suggested edit to this PR, do a separate PR, or otherwise? /cc @AlanBateman (any recommendation, Alan? 🤔 )

[Martin-Buchholz]

@Martin-Buchholz Martin, how would you like to proceed with your proposed wording, would you prefer a suggested edit to this PR, do a separate PR, or otherwise? /cc @AlanBateman (any recommendation, Alan? thinking )

Talked me into it - I will dust off my github/skara skillz and make a new PR.

I wonder if there's now a way to override javadoc for remove() without creating a new method body.

[viktorklang-ora]

@Martin-Buchholz I guess remove could be overridden and just delegate to super?

[Martin-Buchholz]

I wonder if there's now a way to override javadoc for remove() without creating a new method body.

I thought recent javadoc features might have been useful here, but I scanned the results from this jql:

subcomponent in ( "javadoc(tool)", "doclet" )  AND (resolution in ( Fixed, Approved ) ) AND issuetype in (JEP, Enhancement) ORDER BY resolved  DESC

and came up empty

[viktorklang-ora]

Perhaps @pavelrappo has any suggestion for adding clarifying Javadoc to a subclass without having to override the method? 🤔

[pavelrappo]

Perhaps @pavelrappo has any suggestion for adding clarifying Javadoc to a subclass without having to override the method? 🤔

You cannot do that.

[viktorklang-ora]

@Martin-Buchholz @pavelrappo OTOH I see that DelayQueue has already overridden remove(Object o) so you should be able to modify that?

[Martin-Buchholz]

@Martin-Buchholz @pavelrappo OTOH I see that DelayQueue has already overridden remove(Object o) so you should be able to modify that?

Right. But remove(Object) unlike remove() doesn't consider the expiration time. Confusing!

[Martin-Buchholz]

Right. But remove(Object) unlike remove() doesn't consider the expiration time. Confusing!

Actually, confusion extends to three methods with the same name:

• Queue.remove()
• Collection.remove(Object)
• Iterator.remove()

[viktorklang-ora]

@Martin-Buchholz Oh that remove() :)

[openjdk]

@viktorklang-ora this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout 8297605
git fetch https://git.openjdk.org/jdk.git master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

[viktorklang-ora]

Superseded by #12838